Just a few facts to think about,

WB & commodores all went to cross flow radiator design because the tubes weren't long enough in the conventional top & bottom tank radiators, and the coolant didn't stay in the tubes long enough to get cooled when the engine was under load. With car design changing to even lower aerodynamic front end designs the only way was across (crossflow design) to lengthen the coolant passing time in tube to cool. I have found that five core radiators didn't do much for cooling either. Three core radiators are usually more efficient. By the time the 4th&5th tubes get air flow from the previous tubes the air is so hot it makes them inefficient. The other problem is its harder for the air to travel through very thick cores and for that reason they are more restrictive and clog fins more easily. Most car radiators are either single or 2 row aluminium radiators these days. Aluminium radiators transfer heat much better but generally don't have as long service life.

My preferred radiator is the old brass copper units, 2 or 3 row well made core with lots of fins per inch between the tubes. When ever I get presented with an overheating vehicle the first things I check is the fan and shroud operation, restricted or blocked outer fins, heat gun test, coolant condition and level, pressure test, gas test for carbon monoxide in the cooling system. These check only take around 10 minutes. If no obvious things are found with these basic checks. and tests, I remove the radiator and send it out for the local radiator company to service the radiator. This service must include removing the top and bottom tanks and visually check and clean out every tube. I have been caught out a few times over the years when so call good radiator company's flush and paint them black. You put the radiator back in and have the same problem and you naturally think it can't be the radiator, and you can easily spend lots of time and money chasing the problem and all along its as simple as blocked radiator internal core tubes. I generally recommend radiator servicing every five years for regular used vehicles. Many coolant in the past have caused tubes to block up and crystalize in the tubes.

I hope the above helps you to make a better informed approach to cooling system overheating diagnosis.

P.S always insure the gauges are accurate in the car before jumping to a conclusion.

Lenny.